THE APPARITION AND SUCCESSION OF ANIMAL FORMS.

Time was when naturalists were content to take nature as they found it, without any over-curious inquiries as to the origin of its several parts, or the changes of which they might be susceptible. Geology first removed this pleasant state of repose, by showing that all our present species had a beginning, and were preceded by others, and these again by others. Geologists were, however, too much occupied with the facts of the succession to speculate on the ultimate causes of the appearance and disappearance of species, and it remained for zoologists and botanists, or as some prefer to call themselves, biologists, to construct hypotheses or theories to account for the ascertained fact that successive dynasties of species have succeeded each other in time. I do not propose in this paper so much to deal with the various doctrines as to derivation and development now current, as to ask the question, What do we actually know as to the origin and history of life on our planet?

This great question, confessedly accompanied with many difficulties and still waiting for its full solution, has points of intense interest both for the Geologist and the Biologist. "If," says the great founder of the uniformitarian School of Geology, "the past duration of the earth be finite, then the aggregate of geological epochs, however numerous, must constitute a mere moment of the past, a mere infinitesimal portion of eternity." Yet to our limited vision, the origin of life fades away in the almost illimitable depths of past time, and we are ready to despair of ever reaching, by any process of discovery, to its first steps of progress. At what time did life begin? In what form did dead matter first assume or receive those mysterious functions of growth, reproduction and sensation? Only when we picture to ourselves an absolutely lifeless world, destitute of any germ of life or organization, can we realize the magnitude of these questions, and perceive how necessary it is to limit their scope if we would hope for any satisfactory answer.

We may here dismiss altogether that form in which these questions present themselves to the biologist, when he experiments as to the evolution of living forms from dead liquids or solids attacking the unsolved problem of spontaneous generation. Nor need we enter on the vast field of discussion as to modern animals and plants opened up by Darwin and others. I shall confine myself altogether to that historical or palÆontological aspect in which life presents itself when we study the fossil remains entombed in the sediments of the earth's crust, and which will enable me at least to show why some students of fossils hesitate to give in their adhesion to any of the current notions as to the origin of species. It will also be desirable to avoid, as far as possible, the use of the term "evolution," as this has recently been employed in so many senses, whether of development or causation, as to have become nearly useless for any scientific purpose; and that when I speak of creation of species, the term is to be understood not in the arbitrary sense forced on it by some modern writers, but as indicating the continuous introduction of new forms of life under definite laws, but by a power not emanating from within themselves, nor from the inanimate nature surrounding them.[68]

If we were to follow the guidance of those curious analogies which present themselves when we consider the growth of the individual plant or animal from the spore or the ovum, and the development of vegetable and animal life in geological time—analogies which, however, it must be borne in mind can have no scientific value whatever, inasmuch as that similarity of conditions which alone can give force to reasoning from analogy in matters of science, is wholly wanting—we should expect to find in the oldest rocks embryonic forms alone, but of course embryonic forms suited to exist and reproduce themselves independently.[69]

I need not say to palÆontologists that this is not what we actually find in the primordial rocks. I need but to remind them of the early and remarkable development of such forms as the Trilobites, the LingulidÆ and the Pteropods, all of them highly complex and specialized types, and remote from the embryonic stages of the groups to which they severally belong. In the case of the Trilobites, one need merely consider the beautiful symmetry of their parts, both transversely and longitudinally, their division into distinct regions, the necessary complexity of their muscular and nervous systems, their highly complex visual organs, the superficial ornamentation and microscopic structure of their crusts, their advanced position among Crustaceans, indicated by their strong affinity with the Arachnidans or spiders and scorpions. (See figures prefixed.)

All these characters give them an aspect far from embryonic, while, as Barrande has pointed out, this advanced position of the group has its significance greatly strengthened by the fact that in early primordial times we have to deal not with one species, but with a vast and highly differentiated group, embracing forms of many and varied subordinate types. As we shall see, these and other early animals may be regarded as of generalized types, but not as embryonic. Here, then, meets us at the outset the fact that in as far as the great groups of annulose and molluscous animals are concerned, we can trace these back no farther than to a period in which they appear already highly advanced, much specialized and represented by many diverse forms. Either, therefore, these great groups came in on this high initial plane, or we have scarcely reached half way back in the life-history of our planet.

We have, here, however, by this one consideration, attained at once to two great and dominant laws regulating the history of life. First, the law of continuity, whereby new forms come in successively, throughout geological time, though, as we shall see, with periods of greater or less frequency. Secondly, the law of specialization of types, whereby generalized forms are succeeded by those more special, and this probably connected with the growing specialization of the inorganic world. It is this second law which causes the parallelism between the history of successive species and that of the embryo.

We have already considered the claims which Eozoon and its contemporaries may urge to recognition, as beginnings of life; but when we ascend from the Laurentian beds, we find ourselves in a barren series of conglomerates, sandstones, and other rocks, indicating shore rather than sea conditions, and remarkably destitute of indications of life. These are the Huronian beds, and possibly other series associated with them. They have afforded spicules of sponges, casts of burrows of worms, obscure forms, which may represent crustaceans or mollusks, markings of unknown origin, and some laminated forms which may perhaps represent remains of Eozoon, though their structures are imperfectly preserved. These are sufficient to show that marine life continued in some forms, and to encourage the hope that a rich pre-Cambrian fauna may yet be discovered.

But let us leave for the present the somewhat isolated case of Eozoon, and the few scattered forms of the Huronian, and go on farther to the early Cambrian fauna. This is graphically presented to us in the sections in South Wales, as described by Hicks. Here we find a nucleus of ancient rocks, supposed to be Laurentian, though in mineral character more nearly akin to the Huronian, but which have hitherto afforded no trace of fossils. Resting unconformably on these is a series of slates and sandstones, regarded as Lower Cambrian, the Caerfai group of Hicks, and which are the earliest holding organic remains. The lowest bed which contains indications of life is a red shale near the base of the series, which holds a few organic remains. The species are a Lingulella, worm burrows and a Trilobite.[70] Supposing these to be all, it is remarkable that we have no Protozoa or Corals or Echinoderms, and that the types of Brachiopods and Crustaceans are of comparatively modern affinities. Passing upward through 1,000 feet of barren sandstone and shale, we reach a zone in which many Trilobites of at least five genera are found, along with Pteropods, Brachiopods and Sponges. Thus it is that life comes in at the base of the Cambrian in Wales, and it may be regarded as a fair specimen of the facts as they appear in the earlier fossiliferous beds succeeding the Laurentian. Taking the first of these groups of fossils, we may recognise in the worms representatives of those that still haunt our shores, in the Trilobite a Crustacean or Arachnoid of no mean grade. The LingulellÆ, whether we regard them as molluscoids, or, with Professor Morse, as singularly specialized worms, represent a peculiar and distinct type, handed down, through all the vicissitudes of the geological ages, to the present day. Had the Primordial life begun with species altogether inscrutable and unexampled in succeeding ages, this would no doubt have been mysterious; but next to this is the mystery of the oldest forms of life being also among the newest. One great fact shines here with the clearness of noon-day. Whatever the origin of these creatures, they represent families which have endured till now in the struggle for existence without either elevation or degradation. Here, again, we may formulate another creative law. In every great group there are some forms much more capable of long continuance than others. Lingula among the Brachiopods is a marked instance.

But when, with Hicks, we surmount the mass of barren beds underlying these remains, which from its unfossiliferous character is probably a somewhat rapid deposit of Arctic mud, like that which in all geological time has constituted the rough filling of our continental formations, and have suddenly sprung upon us many genera of Trilobites, including the fewest-jointed and most many-jointed, the smallest and the largest of their race, our astonishment must increase, till we recognise the fact that we are now in the presence of another great law of creation, which provides that every new type shall be rapidly extended to the extreme limits of its power of adaptation.

That this is not merely local is evidenced by the researches of Matthew and Walcott in the oldest Cambrian of America, where a similar succession occurs, but with this difference, that in the wider area presented by the American continent we find a greater variety of forms of life. Walcott records up to 1892 no less than 67 genera and 165 species in the oldest Cambrian of America. These include representatives of the Sponges, Hydroids, Corals, Echinoderms, Worms, Brachiopods, Bivalve and Univalve Mollusks and Crustaceans, or in other words, all the leading groups of invertebrate animals that we find in the sea at present. Of these the dominant group is the Crustaceans, including Trilobites, numbering one-third of the whole; and these with the univalve Mollusks and the Brachiopods constitute the majority, the other groups having comparatively few species. What a marvellous incoming of life is here! Walcott may well say that on the theory of gradual development we must suppose that life existed at a period far before the Cambrian—as far, indeed, as the Cambrian is before our own time. But this would mean that we know only half of the history of life; and perhaps it is more reasonable to suppose that when the conditions became favourable, it came in with a rush.

Before considering the other laws that may be inferred from these facts, however, let us in imagination transfer ourselves back to the Primordial age, and suppose that we have in our hands a living specimen of one of the larger Trilobites, recently taken from the sea, flapping vigorously its great tail, and full of life and energy; an animal larger and heavier than the modern king-crab of our shores, furnished with all the complexity of external parts for which the crustaceans are so remarkable, and no doubt with instincts and feelings and modes of action as pronounced as those of its modern allies, and, if Woodward's views are correct, on a higher plane of rank than the king-crab itself, inasmuch as it is a composite type connecting Limuli with Isopods, and even with scorpions. We have obviously here, in the appearance of this great Crustacean or Arachnoid, a repetition of the facts which we met with in Eozoon; but how vast the interval between them in geological time, and in zoological rank! Standing in the presence of this testimony, I think it is only right to say that we possess no causal solution of the appearance of these early forms of life; but in tracing them and their successors upward through the succeeding ages, we may hope at least to reach some expressions of the laws of their succession, in possession of which we may return to attack the mystery of their origin.

First, it must strike every observer that there is a great sameness of plan throughout the whole history of marine invertebrate life. If we turn over the pages of an illustrated text-book of geology, or examine the cases or drawers of a collection of fossils, we shall find extending through every succeeding formation, representative forms of Crustaceans, Mollusks, Corals, etc., in such a manner as to indicate that in each successive period there has been a reproduction of the same type with modifications; and if the series is not continuous, this appears to be due rather to abrupt physical changes; since sometimes, where two formations pass into each other, we find a gradual change in the fossils by the dropping out and introduction of species one by one. Thus, in the whole of the great PalÆozoic Period, both in its Fauna and Flora, we have a continuity and similarity of a most marked character.

It is evident that there is presented to us in this similarity of the forms of successive faunas and floras, a phenomenon which deserves very careful sifting as to the question of identity or diversity of species. The data for its comprehension must be obtained by careful study of the series of closely allied forms occurring in successive formations, and the great and undisturbed areas of the older rocks in America seem to give special facilities for this, which should be worked, not in the direction of constituting new species for every slightly divergent form, but in striving to group these forms into large specific types.[71]

There is nothing to preclude the supposition that some of the groups mentioned in the note are really specific types, with numerous race modifications. My own provisional conclusion, based on the study of PalÆozoic plants, is that the general law will be found to be the existence of distinct specific types, independent of each other, but liable in geological time to a great many modifications, which have often been regarded as distinct species.[72]

While this unity of successive faunÆ at first sight presents an appearance of hereditary succession, it loses much of this character when we consider the number of new types introduced without apparent predecessors, the necessity that there should be similarity of type in successive faunÆ on any hypothesis of a continuous plan; and above all, the fact that the recurrence of representative species or races in large proportion marks times of decadence rather than of expansion in the types to which they belong. To turn to another period, this is very manifest in that singular resemblance which obtains between the modern mammals of South America and Australia, and their immediate fossil predecessors—the phenomenon being here manifestly that of decadence of large and abundant species into a few depauperated representatives. This will be found to be a very general law, elevation being accompanied by the apparent abrupt appearance of new types and decadence by the apparent continuation of old species, or modifications of them.

This resemblance with difference in successive faunas also connects itself very directly with the successive elevations and depressions of our continental plateaus in geological time. Every great PalÆozoic limestone, for example, indicates a depression with succeeding elevation. On each elevation marine animals were driven back into the ocean, and on each depression swarmed in over the land, reinforced by new species, either then introduced, or derived by migration from other localities. In like manner, on every depression, land plants and animals were driven in upon insular areas, and on re-elevation, again spread themselves widely. Now I think it will be found to be a law here that periods of expansion were eminently those of introduction of new specific types, and periods of contraction those of extinction, and also of continuance of old types under new varietal forms.

It must also be noticed that all the leading types of invertebrate life were early introduced, that change within these was necessarily limited, and that elevation could take place mainly by the introduction of the vertebrate orders. So in plants, Cryptogams early attained their maximum as well as Gymnosperms, and elevation occurred in the introduction of PhÆnogams, and this not piecemeal, but as we shall see in a succeeding chapter, in great force at once.

We may further remark the simultaneous appearance of like types of life in one and the same geological period, over widely separated regions of the earth's surface. This strikes us especially in the comparatively simple and homogeneous life-dynasties of the PalÆozoic, when, for example, we find the same types of Silurian Graptolites, Trilobites and Brachiopods appearing simultaneously in Australia, America and Europe. Perhaps in no department is it more impressive than in the introduction of the Devonian and Carboniferous Ages of that grand cryptogamous and gymnospermous flora which ranges from Brazil to Spitzbergen, and from Australia to Scotland, accompanied in all by the same groups of marine invertebrates. Such facts may depend either on that long life of specific types which gives them ample time to spread to all possible habitats, before their extinction, or on some general law whereby the conditions suitable to similar types of life emerge at one time in all parts of the world. Both causes may be influential, as the one does not exclude the other, and there is reason to believe that both are natural facts. Should it be ultimately proved that species allied and representative, but distinct in origin, come into being simultaneously everywhere, we shall arrive at one of the laws of creation, and one probably connected with the gradual change of the physical conditions of the world.

Another general truth, obvious from the facts which have been already collected, is the periodicity of introduction of species. They come in by bursts or flood tides at particular points of time, while these great life waves are followed and preceded by times of ebb in which little that is new is being produced. We labour in our investigation of this matter under the disadvantage that the modern period is evidently one of the times of pause in the creative work. Had our time been that of the early Tertiary or early Mesozoic, our views as to the question of origin of species might have been very different. It is a striking fact, in illustration of this, that since the glacial age no new species of mammal, except, possibly, man himself, can be proved to have originated on our continents, while a great number of large and conspicuous forms have disappeared. It is possible that the proximate or secondary causes of the ebb and flow of life production may be in part at least physical, but other and more important efficient causes may be behind these. In any case these undulations in the history of life are in harmony with much that we see in other departments of nature.

It results from the above and the immediately preceding statement, that specific and generic types enter on the stage in great force, and gradually taper off towards extinction. They should so appear in the geological diagrams made to illustrate the succession of living beings. This applies even to those forms of life which come in with fewest species and under the most humble guise. What a remarkable swarming, for example, there must have been of Marsupial Mammals in the early Mesozoic, and in the Coal formation the only known Pulmonate snails, five or six in number, belong to four generic types, while the Myriapods and Amphibians alike appear in a crowd of generic forms.

I have already referred to the permanence of species in geological time. We may now place this in connection with the law of rapid origination and more or less continuous transmission of varietal forms. A good illustration will be afforded by a group of species with which I am very familiar, that which came into our seas at the beginning of the Glacial age, and still exists. With regard to their permanence, it can be affirmed that the shells now elevated in Wales to 1,200, and in Canada to 600 feet above the sea, and which lived before the last great revolution of our continents a period very remote as compared with human history—differ in no tittle from their modern successors after hundreds or thousands of generations. It can also be affirmed that the more variable species appear under precisely the same varietal forms then as now, though these varieties have changed much in their local distribution. The real import of these statements, which might also be made with regard to other groups, well known to palÆontologists, is of so great significance that it can be realized only after we have thought of the vast time and numerous changes through which these humble creatures have survived. I may call in evidence here a familiar New England animal, the common sand clam, Mya arenaria, and its relative Mya truncata, the short sand clam, which now inhabit together all the northern seas; for the Pacific specimens, from Japan and California, though differently named, are undoubtedly the same. Mya truncata appears in Europe in the Coralline Crag, and was followed by M. arenaria in the Red Crag. Both shells occur in the Pleistocene of America, and their several varietal forms had already developed themselves in the Crag, and remain the same to-day; so that these humble mollusks, littoral in their habits, and subjected to a great variety of conditions, have continued for a very long period to construct their shells precisely as at present; while in many places, as on the Lower St. Lawrence, we find them living together on the same banks, and yet preserving their distinctness.[73] Nor are there any indications of a transition between the two species. I might make similar statements with regard to the Astartes, Buccinums and TellinÆ of the drift, and could illustrate them by extensive series of specimens from my own collections.

Another curious illustration is that presented by the Tertiary and modern faunÆ of some oceanic islands far separated from the continents. In Madeira and Porto Santo, for example, according to Lyell, we have fifty-six species of land shells in the former, and forty-two in the latter, only twelve being common to the two, though these islands are only thirty miles apart. Now in the Pliocene strata of Madeira and Porto Santo we find thirty-six species in the former, and thirty-five in the latter, of which only eight per cent, are extinct, and yet only eight are common to the two islands. Further, there seem to be no transitional forms connecting the species, and of some of them the same varieties existed in the Pliocene as now. The main difference in time is the extinction of some species and the introduction of others without known connecting links, and the fact that some species, plentiful in the Pliocene, are rare now, and vice versÂ. All these shells differ from those of modern Europe, but some of them are allied to Miocene species of that continent. Here we have a case of continued existence of the same forms, and in circumstances which, the more we think of them, the more do they defy all our existing theories as to specific origins.

Perhaps some of the most remarkable facts in connection with the permanence of varietal forms of species are those furnished by that magnificent flora which burst in all its majesty on the American continent in the Cretaceous period, and still survives among us, even in some of its specific types. I say survives; for we have but a remnant of its forms living, and comparatively little that is new has probably been added since. The confusion which has obtained as to the age of this flora, and its mistaken reference to the Miocene Tertiary, have arisen in part from the fact that this modern flora was in its earlier times contemporary with Cretaceous animals, and survived the gradual change from the animal life of the Cretaceous down to that of the Eocene, and even of the Miocene. In collections of these plants, from what may be termed beds of transition from the Cretaceous to the Tertiary, we find many plants of modern species, or so closely related that they may be mere varietal forms. Some of these will be mentioned in the next paper, and they show that modern plants, some of them small and insignificant, others of gigantic size, reach back to a time when the Mesozoic Dinosaurs were becoming extinct, and the earliest Placental mammals being introduced. Shall we say that these plants have propagated themselves unchanged for half a million of years, or more?[74]

Take from the western Mesozoic a contrasting yet illustrative fact. In the lowest Cretaceous rocks of Queen Charlotte's Island, Mr. Richardson and Dr. G. M. Dawson find Ammonites and allied Cephalopods similar in many respects to those discovered farther south by the California Survey, and Mr. Whiteaves finds that some of them are apparently not distinct from species described by the PalÆontologists of the Geological Survey of British India. On both sides of the Pacific these shells lie entombed in solid rock, and the Pacific rolls between, as of yore. Yet these species, genera, and even families are all extinct why, no man can tell, while land plants that must have come in while the survivors of these Cephalopods still lived, reach down to the present. How mysterious is all this, and how strongly does it show the independence in some sense of merely physical agencies on the part of the manifestations of life!

We have naturally been occupied hitherto with the lower tribes of animals and with plant life, because these are predominant in the early ages of the earth. Let us turn now to the history of vertebrate or back-boned animals, which presents some peculiarities special to itself. Many years ago Pander[75] described and figured from the Cambro-Silurian of Russia, a number of minute teeth, some conical and some comb-like, which he referred to fishes, and to that low form of the fish type represented by the modern lampreys. Much doubt was thrown on this determination, more especially as the teeth seemed to be composed not of bone earth, but of carbonate of lime, and it was suggested that they may have belonged to marine worms, or to the lingual ribbons of Gastropod mollusks. Some confirmatory evidence seems to have been supplied by the discovery of great numbers of similar forms in the shales of the coal formation of Ohio, by the late Dr. Newberry. I have had an opportunity to examine these, and find that they consist of calcium phosphate,[76] or bone earth, and that their microscopic structure is not dissimilar from that of the teeth of some of the smaller sharks (Diplodus) found with them. I have therefore been inclined to believe that there may have already been, even in the Cambrian or Lower Silurian seas, true fishes, related partly to the lampreys and partly to sharks; so that the history of the back-boned animals may have gone nearly as far back as that of their humbler relations. This conjecture has recently received further support from the discovery in rocks of Lower Silurian age, in Colorado of a veritable bone bed, rich in fragmentary remains of fishes. They are unfortunately so comminuted as to resemble the dÉbris of the food of some larger animal; but in so far as I can judge from specimens kindly given to me,[77] they resemble the bony coverings of some of the familiar fishes of the Devonian. Thus they would indicate, with Pander's and Rohan's specimens, already two distinct types of fishes as existing almost as early as the higher invertebrates of the sea.

In the Silurian (Upper Silurian of Murchison) we have undoubted evidence of the same kind, on both sides of the Atlantic, in teeth and spines of sharks, and the plates which protected the heads and bodies of the plate-covered fishes (Placo-ganoids). But it is in the Devonian that these types appear to culminate, and we have added to them that remarkable type of "lung fish," as the Germans call them, represented in our modern world only by the curious and exceptional Burramunda of Australia, and the mud fishes of Africa and South America,[78] creatures which show, as do some of the mailed fishes, or ganoids, of equally great age, the intermediate stages between a swimming bladder and a lung, and thus approach nearer to the air-breathing animals than any other fishes.

Many years ago, in "Acadian Geology," I referred to the probability that the mailed and lung fishes of the Devonian and Carboniferous possessed air bladders so constructed as to enable them to breathe air, as is the case with their modern representatives. In the modern species this, no doubt, enables them to haunt badly aËrated waters, in swamps and sluggish streams, and in some cases even to survive when the water in which they live is dried up. In the Carboniferous and Devonian it may have served a similar purpose, fitting them to inhabit the lagoons and creeks of the coal swamps, the water of which must often have been badly aËrated. It makes against this that some sharks followed them into these waters, and the modern sharks have no swim-bladders. Possibly, however, the sharks habitually haunted the open sea, and only made occasional raids on the dangerous waters tenanted by the ganoids. It is also true that only certain genera of sharks are found to be represented in the carbonaceous shales, and they may have differed in this respect from the ordinary forms of the order. It has been suggested that only a small change would be necessary to enable some of these lung fishes to become Batrachians, and no doubt this is the nearest approach of the fish to the reptile; but we have not yet found connecting links sufficient to bridge over the whole distance.

The plate-bearing ganoids of the Silurian and Devonian, at one time supposed to be allied to Crustaceans, but whose dignity as "Forerunners of the back-boned animals" is now generally admitted,[79] are clearly true fishes, and of somewhat high rank, their strange bony armour being evidently a special protection against the attacks of contemporary sharks and gigantic crustaceans; and if we may judge by the Colorado specimens, their existence dates back almost to the close of the Cambrian, and they were probably contemporary with small sharks; while as early as the Silurian and Devonian, if we regard the scaly ganoids as a distinct type, we have already four types of fishes, and these akin to those which in modern time we must regard as the highest of their class.

One very little fish of the Devonian, of which specimens have been kindly sent me by a friend in Scotland,[80] the PalÆospondylus of Traquair, may raise still higher hopes for the early vertebrates. It is a little creature, an inch to two inches in length, destitute or nearly destitute of bony covering, having a head which suggests the presence of external gills, large eyes, and even elongated nasal bones,[81] a long vertebral column composed of separate bony rings, more than fifty in number, with possible indications of ribs in front and distinct neural and haemal processes behind. One cannot look at it without the suggestion occurring of some of the smaller snake-like Batrachians of the Carboniferous and Permian; and I should not be surprised if it should come to be regarded either as a forerunner of the Batrachians or as a primitive tadpole.

However this may be, the upper part of the Devonian, though rich in fishes and plants, has afforded no higher vertebrates than its lower parts, and in the lowest Carboniferous beds we suddenly find ourselves in the presence of Batrachians with well-developed limbs and characters which ally them to the Lizards. True lizard-like reptiles appear in the Permian, and then we enter on that marvellous reign of reptiles, in which this class assumed so many great and remarkable forms, and asserted itself in a manner of which the now degraded reptilian class can afford no conception.

The mammals and birds make their first appearance quietly in small and humble forms in the reign of reptiles, in which there was little place left for them by the latter; but the mammals burst upon us in all their number and magnitude in the Eocene and Miocene, in which quadrupedal mammalian life may be said to have culminated in grandeur, variety, and geographical distribution; far excelling in these respects the time in which we live.

The development in time of the back-boned animals thus stands in some degree by itself; but it illustrates the same laws of early generalised types, and sudden and wide introduction of new forms, which we have seen in the case of the invertebrates and the plants.

Such facts as those to which I have referred, and many others, which want of space prevents me from noticing, are in one respect eminently unsatisfactory, for they show us how difficult must be any attempts to explain the origin and succession of life. For this reason they are quietly put aside or explained away in most of the current hypotheses on the subject. But we must, as men of science, face these difficulties, and be content to search for facts and laws, even if they should prove fatal to preconceived views.

A group of new laws, indeed, here breaks upon us. (1) The great vitality and rapid extension and variation of new specific types. (2) The law of spontaneous decay and mortality of species in time. (3) The law of periodicity and of simultaneous appearance of many allied forms. (4) The abrupt entrance and slow decay of groups of species. (5) The extremely long duration of some species in time. (6) The grand march of new forms landwards, and upwards in rank. Such general truths deeply impress us at least with the conclusion that we are tracing, not a fortuitous succession, but the action of power working by law.

I have thus far said nothing of the bearing of the prevalent ideas of descent with modification on this wonderful procession of life. None of these, of course, can be expected to take us back to the origin of living beings; but they also fail to explain why so vast numbers of highly organized species struggle into existence simultaneously in one age and disappear in another, why no continuous chain of succession in time can be found gradually blending species into each other, and why, in the natural succession of things, degradation under the influence of external conditions and final extinction seem to be laws of organic existence. It is useless here to appeal to the imperfection of the record, or to the movements or migrations of species. The record is now, in many important parts, too complete, and the simultaneousness of the entrance of the faunas and floras too certainly established, and moving species from place to place only evades the difficulty. The truth is that such hypotheses are at present premature, and that we require to have larger collections of facts. Independently of this, however, it appears to me that from a philosophical point of view it is extremely probable that all theories of evolution, as at present applied to life, are fundamentally defective in being too partial in their character; and perhaps I cannot better group the remainder of the facts to which I wish to refer than by using them to illustrate this feature of most of our attempts at generalization on this subject.

First, then, these hypotheses are too partial, in their tendency to refer numerous and complex phenomena to one cause, or to a few causes only, when all trustworthy analogy would indicate that they must result from many concurrent forces and determinations of force. We have all, no doubt, read those ingenious, not to say amusing, speculations in which some entomologists and botanists have indulged with reference to the mutual relations of flowers and suctorial insects. Geologically the facts oblige us to begin with Cryptogamous plants and chewing insects, and out of the desire of insects for non-existent honey, and the adaptations of plants to the requirements of non-existent suctorial apparatus, we have to evolve the marvellous complexity of floral form and colouring, and the exquisitely delicate apparatus of the mouths of haustellate insects. Now, when it is borne in mind that this theory implies a mental confusion on our part precisely similar to that which, in the department of mechanics, actuates the seekers for perpetual motion, that we have not the smallest tittle of evidence that the changes required have actually occurred in any one case, and that the thousands of other structures and relations of the plant and the insect have to be worked out by a series of concurrent developments so complex and absolutely incalculable in the aggregate, that the cycles and epicycles of the Ptolemaic astronomy were child's play in comparison, we need not wonder that the common sense of mankind revolts against such fancies, and that we are accused of attempting to construct the universe by methods that would baffle Omnipotence itself, because they are simply absurd. In this aspect of them, indeed, such speculations are necessarily futile, because no mind can grasp all the complexities of even any one case, and it is useless to follow out an imaginary line of development which unexplained facts must contradict at every step. This is also, no doubt, the reason why all recent attempts at constructing "Phylogenies" are so changeable, and why no two experts can agree about almost any of them.

A second aspect in which such speculations are too partial, is in the unwarranted use which they make of analogy. It is not unusual to find such analogies as that between the embryonic development of the individual animal and the succession of animals in geological time placed on a level with that reasoning from analogy by which geologists apply modern causes to explain geological formations. No claim could be more unfounded. When the geologist studies ancient limestones built up of the remains of corals, and then applies the phenomena of modern coral reefs to explain their origin, he brings the latter to bear on the former by an analogy which includes not merely the apparent results, but the causes at work, and the conditions of their action, and it is on this that the validity of his comparison depends, in so far as it relates to similarity of mode of formation. But when we compare the development of an animal from an embryo cell with the progress of animals in time, though we have a curious analogy as to the steps of the process, the conditions and causes at work are known to be altogether dissimilar, and therefore we have no evidence whatever as to identity of cause, and our reasoning becomes at once the most transparent of fallacies. Further, we have no right here to overlook the fact that the conditions of the embryo are determined by those of a previous adult, and that no sooner does this hereditary potentiality produce a new adult animal, than the terrible external agencies of the physical world, in presence of which all life exists, begin to tell on the organism, and after a struggle of longer or shorter duration it succumbs to death, and its substance returns into inorganic nature, a law from which even the longer life of the species does not seem to exempt it. All this is so plain and manifest that it is extraordinary that evolutionists will continue to use such partial and imperfect arguments. Another illustration may be taken from that application of the doctrine of natural selection to explain the introduction of species in geological time, which is so elaborately discussed by Sir C. Lyell in the last edition of his "Principles of Geology." The great geologist evidently leans strongly to the theory, and claims for it the "highest degree of probability," yet he perceives that there is a serious gap in it; since no modern fact has ever proved the origin of a new species by modification. Such a gap, if it existed in those grand analogies by which he explained geological formations through modern causes, would be admitted to be fatal.

A third illustration of the partial character of these hypotheses may be taken from the use made of the theory deduced from modern physical discoveries, that life must be merely a product of the continuous operation of physical laws. The assumption for it is nothing more that the phenomena of life are produced merely by some arrangement of physical forces, even if it be admitted to be true, gives only a partial explanation of the possible origin of life. It does not account for the fact that life, as a force, or combination of forces, is set in antagonism to all other forces. It does not account for the marvellous connection of life with organization. It does not account for the determination and arrangement of forces implied in life. A very simple illustration may make this plain. If the problem to be solved were the origin of the mariner's compass, one might assert that it is wholly a physical arrangement, both as to matter and force. Another might assert that it involves mind and intelligence in addition. In some sense both would be right. The properties of magnetic force and of iron or steel are purely physical, and it might even be within the bounds of possibility that somewhere in the universe a mass of natural lodestone may have been so balanced as to swing in harmony with the earth's magnetism. Yet we would surely be regarded as very credulous if we could be induced to believe that the mariner's compass has originated in that way. This argument applies with a thousandfold greater force to the origin of life, which involves even in its simplest forms so many more adjustments of force and so much more complex machinery.

Fourthly, these hypotheses are partial, inasmuch as they fail to account for the vastly varied and correlated interdependencies of natural things and forces, and for the unity of plan which pervades the whole. These can be explained only by taking into the account another element from without. Even when it professes to admit the existence of a God, the evolutionist reasoning of our day contents itself altogether with the physical or visible universe, and leaves entirely out of sight the power of the unseen and spiritual, as if this were something with which science has nothing to do, but which belongs only to imagination or sentiment. So much has this been the case, that when recently a few physicists and naturalists have referred to the "Unseen Universe," they have seemed to be teaching new and startling truths, though only reviving some of the oldest and most permanent ideas of our race. From the dawn of human thought it has been the conclusion alike of philosophers, theologians, and the common sense of mankind, that the seen can be explained only by reference to the unseen, and that any merely physical theory of the world is necessarily partial. This, too, is the position of our sacred Scriptures, and is broadly stated in their opening verse, and indeed it lies alike at the basis of all true religion and all sound philosophy, for it must necessarily be that "the things that are seen are temporal, the things that are unseen, eternal." With reference to the primal aggregation of energy in the visible universe, with reference to the introduction of life, with reference to the soul of man, with reference to the heavenly gifts of genius and prophecy, with reference to the introduction of the Saviour Himself into the world, and with reference to the spiritual gifts and graces of God's people, all these spring, not from sporadic acts of intervention, but from the continuous action of God and the unseen world; and this, we must never forget, is the true ideal of creation in Scripture and in sound theology. Only in such exceptional and little influential philosophies as that of Democritus, and in the speculations of a few men carried off their balance by the brilliant physical discoveries of our age, has this necessarily partial and imperfect view been adopted. Never, indeed, was its imperfection more clear than in the light of modern science.

Geology, by tracing back all present things to their origin, was the first science to establish on a basis of observed facts the necessity of a beginning and end of the world. But even physical science now teaches us that the visible universe is a vast machine for the dissipation of energy; that the processes going on in it must have had a beginning in time, and that all things tend to a final and helpless equilibrium. This necessity implies an unseen power, an invisible universe, in which the visible universe must have originated, and to which its energy is ever returning. The hiatus between the seen and the unseen may be bridged over by the conceptions of atomic vortices of force, and by the universal and continuous ether; but whether or not, it has become clear that the conception of the unseen, as existing, has become necessary to our belief in the possible existence of the physical universe itself, even without taking life into account.

It is in the domain of life, however, that this necessity becomes most apparent; and it is in the plant that we first clearly perceive a visible testimony to that unseen which is the counterpart of the seen. Life in the plant opposes the outward rush of force in our system, arrests a part of it on its way, fixes it as potential energy, and thus, forming a mere eddy, so to speak, in the process of dissipation of energy, it accumulates that on which animal life and man himself may subsist, and assert for a time supremacy over the seen and temporal on behalf of the unseen and eternal. I say, for a time, because life is, in the visible universe, as at present constituted, but a temporary exception, introduced from that unseen world where it is no longer the exception but the eternal rule. In a still higher sense, then, than that in which matter and force testify to a Creator, organization and life, whether in the plant, the animal, or man, bear the same testimony, and exist as outposts put forth in the succession of ages from that higher heaven that surrounds the visible universe. In them, too, Almighty power is no doubt conditioned or limited by law; yet they bear more distinctly upon them the impress of their Maker, and, while all explanations of the physical universe which refuse to recognise its spiritual and unseen origin must necessarily be partial and in the end incomprehensible, this destiny falls more quickly and surely on the attempt to account for life and its succession on merely materialistic principles.

Here again, however, we must bear in mind that creation, as maintained against such materialistic evolution, whether by theology, philosophy, or Holy Scripture, is necessarily a continuous, nay, an eternal, influence, not an intervention of disconnected acts. It is the true continuity, which includes and binds together all other continuity.

It is here that natural science meets with theology, not as an antagonist, but as a friend and ally in its time of greatest need; and I must here record my belief that neither men of science nor theologians have a right to separate what God in Holy Scripture has joined together, or to build up a wall between nature and religion, and write upon it, "no thoroughfare." The science that does this must be impotent to explain nature, and without hold on the higher sentiments of man. The theology that does this must sink into mere superstition.

In conclusion, can we formulate a few of the general laws, or perhaps I had better call them the general conclusions, respecting life, in which all PalÆontologists may agree. Perhaps it is not possible to do this at present satisfactorily, but the attempt may do no harm. We may, then, I think, make the following affirmations:—

1. The existence of life and organization on the earth is not eternal, or even coeval with the beginning of the physical universe, but may possibly date from Laurentian or immediately pre-Laurentian ages.

2. The introduction of new species of animals and plants has been a continuous process, not necessarily in the sense of derivation of one species from another, but in the higher sense of the continued operation of the cause or causes which introduced life at first. This, as already stated, I take to be the true theological or Scriptural as well as scientific idea of what we ordinarily and somewhat loosely term creation.

3. Though thus continuous, the process has not been uniform; but periods of rapid production of species have alternated with others in which many disappeared and few were introduced. This may have been an effect of physical cycles reacting on the progress of life.

4. Species, like individuals, have greater energy and vitality in their younger stages, and rapidly assume all their varietal forms, and extend themselves as widely as external circumstances will permit. Like individuals also, they have their periods of old age and decay, though the life of some species has been of enormous duration in comparison with that of others; the difference appearing to be connected with degrees of adaptation to different conditions of life.

5. Many allied species, constituting groups of animals and plants, have made their appearance at once in various parts of the earth, and these groups have obeyed the same laws with the individual and the species in culminating rapidly, and then slowly diminishing, though a large group once introduced has rarely disappeared altogether.

6. Groups of species, as genera and orders, do not usually begin with their highest or lowest forms, but with intermediate and generalized types, and they show a capacity for both elevation and degradation in their subsequent history.

7. The history of life presents a progress from the lower to the higher, and from the simpler to the more complex, and from the more generalized to the more specialized. In this progress new types are introduced, and take the place of the older ones, which sink to a relatively subordinate place, and become thus degraded. But the physical and organic changes have been so correlated and adjusted that life has not only always maintained its existence, but has been enabled to assume more complex forms, and thus older forms have been made to prepare the way for newer, so that there has been, on the whole, a steady elevation culminating in man himself. Elevation and specialization have, however, been secured at the expense of vital energy and range of adaptation, until the new element of a rational and inventive nature was introduced only in the case of man.

8. In regard to the larger and more distinct types, we cannot find evidence that they have, in their introduction, been preceded by similar forms connecting them with previous groups; but there is reason to believe that many supposed representative species in successive formations are really only races or varieties.

9. In so far as we can trace their history, specific types are permanent in their characters from their introduction to their extinction, and their earlier varietal forms are similar to their later ones.

10. PalÆontology furnishes no direct evidence, perhaps never can furnish any, as to the actual transformation of one species into another, or as to the actual circumstances of creation of a species; but the drift of its testimony is to show that species come in per saltum, rather than by any slow and gradual process.

11. The origin and history of life cannot, any more than the origin and determination of matter and force, be explained on purely material grounds, but involve the consideration of power referable to the unseen and spiritual world.

Different minds may state these principles in different ways, but I believe that in so far as palÆontology is concerned, in substance they must hold good, at least as steps to higher truths. And now allow me to say that we should be thankful that it is given to us to deal with so great questions, and that in doing so, deep humiliation, earnest seeking for truth, patient collection of all facts, self-denying abstinence from hasty generalizations, forbearance and generous estimation with regard to our fellow labourers, and reliance on that Divine Spirit which has breathed into us our intelligent life, and is the source of all true wisdom, are the qualities which best become us.

But while the principles noted above may be said to be known laws of the apparition of new forms of life, they do not reach to the secondary efficient causes of the introduction of new species. What these may ultimately prove to be, to what extent they can be known by us, and to what extent they may include processes of derivation, it is impossible now to say. At present we must recognise in the prevailing theories on the subject merely the natural tendency of the human mind to grasp the whole mass of the unknown under some grand general hypothesis, which, though perhaps little else than a figure of speech, satisfies for the moment. We are dealing with the origin of species precisely as the alchemists did with chemistry, and as the Plutonists and Neptunists did with geology; but the hypotheses of to-day may be the parents of investigations which will become real science to-morrow. In the meantime it is safe to affirm that whatever amount of truth there may be in the several hypotheses which have engaged our attention, there is a creative force above and beyond them, and to the threshold of which we shall inevitably be brought, after all their capabilities have been exhausted by rigid investigation of facts. It is also consolatory to know that species, in so far as the Modern period, or any one past geological period may be concerned, are so fixed that for all practical purposes they may be regarded as unchanging. They are to us what the planets in their orbits are to the astronomer, and speculations as to the origin of species are merely our nebular hypotheses as to the possible origin of worlds and systems.

References:—Address as Vice-President of American Association at Detroit, 1875. "The Chain of Life in Geological Time," London, 1879. Addresses to Natural History Society of Montreal, published in Canadian Naturalist, "Apparition of Animal Forms," Princeton Review.

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